Relaxin is a reproductive hormone produced by your ovaries and the placenta. It loosens and relaxes your muscles, joints and ligaments during pregnancy to help your body stretch. Relaxin also helps your body prepare for delivery by loosening the muscles and ligaments in your pelvis. It can make you more prone to injury, but most people never feel its effects.


What is relaxin?

Relaxin is a hormone with a significant role in your reproductive system, especially during pregnancy. Its main job is to "relax" your ligaments and muscles and make them more flexible. Your body produces relaxin during your menstrual cycle. Its purpose is to:

  • Relax your uterus.
  • Prepare your uterine lining for implantation (when the embryo attaches to your uterus).
  • Prevent contractions.

If conception doesn’t occur that menstrual cycle, relaxin goes down until your next menstrual cycle. However, relaxin levels stay high if conception occurs and continue to rise through your first trimester (the first 12 weeks) of pregnancy. During pregnancy, relaxin helps your body stretch to accommodate the growing fetus.

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What does relaxin hormone do?

Your ovaries make relaxin before you become pregnant. It rises in the second half of your menstrual cycle. It also prepares the lining of your uterus so that if fertilization occurs, implantation is more successful. The relaxing properties of relaxin also help prevent uterine contractions (tightening of uterine muscles) during pregnancy.

Relaxin levels continue to rise if you’re pregnant. This is because the placenta will also begin producing relaxin. The placenta is an organ that provides food, nutrients and oxygen to the fetus during pregnancy. Relaxin levels peak at around 12 to 14 weeks of pregnancy.

As the fetus grows in your uterus, relaxin helps your body stretch. It’s helpful during childbirth when your pelvis needs to relax to allow your baby to descend the birth canal. Relaxin also helps to prepare your cervix for labor and delivery.

What are the functions of relaxin during pregnancy?

Relaxin plays a unique role in relaxing your muscles, ligaments and joints during pregnancy. Some of the functions of relaxin during pregnancy include:

  • Helping to prepare the lining of your uterus for implantation.
  • Helping to grow the placenta if implantation occurs.
  • Preventing early contractions and preterm labor by relaxing the uterine muscles.
  • Relaxing ligaments so your uterus can expand to accommodate the pregnancy.
  • Making your abdominal muscles more flexible.
  • Relaxing blood vessels to accommodate for the increase in blood volume during pregnancy.
  • Helping to relax your pelvis before delivery.
  • Helping your cervix soften and expand before delivery.

How does relaxin affect other parts of the body?

Some studies have shown that relaxin can help treat scarring, or when your tissue hardens. It may mean that relaxin can help scarred tissue in other organs like your heart or lungs. Relaxin can also help with inflammation and may help heal injuries. It may have an effect on your blood pressure. Studies show it helps relax blood vessels and helps grow new blood vessels.


When do you start making relaxin during pregnancy?

You make relaxin before pregnancy. It’s in your body at low levels until around ovulation when it starts to rise. Relaxin production soars if you become pregnant and reaches its peak around the end of the first trimester. After that, it will decline for the rest of pregnancy before surging one last time just before delivery. Researchers believe the last surge helps relax your pelvis and widen your cervix.


Where does relaxin come from?

The ovaries secrete relaxin during the second half of your menstrual cycle. If you become pregnant during that cycle, the placenta also begins to secrete relaxin.

No one is sure what causes your body to release relaxin. It may control its own release or depend on other hormones like luteinizing hormone (LH) or human chorionic gonadotrophin (HCG) for its release. LH and HCG are secreted by the pituitary gland and play a critical role in conception and the development of the placenta.


What does relaxin feel like?

You can’t feel relaxin, and it doesn’t usually cause pain. Some people believe its relaxing effect causes gastrointestinal issues because it prevents your intestines from tightening as they usually do. This can cause constipation, bloating or indigestion in some pregnant people.

Relaxin can also weaken your pelvic floor, which may have an effect on bladder control. It can also negatively affect your posture because your back and pelvis are looser.

Relaxin makes you more flexible during pregnancy, which is great for the growing fetus and for delivery. Unfortunately, this can make you more susceptible to injuries and sprains. Take extra care during pregnancy since you are a little more unsteady on your feet. It’s a good idea to stick to gentle exercises and avoid heavy lifting.

What does relaxin help with?

Relaxin serves many roles in your body beginning in the middle of the menstrual cycle. During the first few weeks of pregnancy, it helps the embryo implant into the uterine wall and promotes the growth of the placenta. It helps loosen your muscles and joints, prevent early contractions and helps facilitate blood flow to and from the placenta.

Relaxin levels decrease after the first trimester, but the hormone stays in your body for the remainder of pregnancy and several months after. Relaxin loosens the muscles, joints and ligaments of your pelvis to help make the labor and delivery process easier. It can also help your cervix soften and open before delivery.

Between your growing belly and the loosening effect of relaxin, it’s common to feel unsteady. So be extra careful with exercise and choose gentle movements to avoid overstretching or overusing your muscles.

Conditions and Disorders

Can you have too much or too little relaxin?

Yes, it’s possible to have high or low relaxin. There isn’t a lot of research done on the effects of too little or too much relaxin. Certain studies show that high relaxin can cause premature rupturing of the membranes, leading to premature labor. Low levels of relaxin may cause scleroderma, but there isn’t enough research yet. Scleroderma is a condition where your skin thickens and hardens.

Does relaxin hormone cause health conditions?

Relaxin hasn’t been shown to cause any health conditions. There’s some evidence that people with endometriosis may have low levels of relaxin. Other studies have shown that relaxin may cause heavy bleeding during a person’s menstrual period. More research is needed to confirm either of these studies.


Can relaxin cause joint pain?

Most people don’t notice the effects of relaxin; however, relaxin can cause pelvic pain in some people during pregnancy. This is pregnancy-related pelvic girdle pain (PGP). It may cause you to feel pain when using the stairs, getting out of cars, changing positions in bed or standing on one leg.

People with PGP feel pain:

  • In the front of the pubic bone (at hip level).
  • Across one or both sides of the lower back.
  • In the perineum (area between your vagina and anus).
  • In the inner thighs.

Relaxin causes most of the muscles and ligaments around your pelvis, back and abdomen to loosen. This can make you feel weak or unstable. Some people find that wearing a belly band during pregnancy offers additional support and helps with posture.

How long do you have relaxin in your body after delivery?

The level of relaxin in your body drops after birth but remains at a decreased level for several months. Some sources say it can take up to 12 months for relaxin levels to return to pre-pregnancy levels. This means you should continue to be cautious with exercise because your ligaments and joints will still be loose. You may feel the effects of relaxin even longer if you are breastfeeding (chestfeeding).

A note from Cleveland Clinic

Relaxin plays a special role in your body, especially during pregnancy. It helps to relax and loosen your joints, muscles and ligaments. It helps your body expand during pregnancy and makes delivering your baby a little easier. Most people don’t feel the side effects of relaxin; however, it can cause pain and make you more prone to injuries. Talk to your healthcare provider if you experience any pelvic pain during pregnancy so they can be sure it’s nothing to worry about.

Medically Reviewed

Last reviewed on 10/17/2022.

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